Wafer cleaning

ABSTRACT

Semiconductor wafers are cleaned using megasonic energy to agitate cleaning fluid applied to the wafer. A source of energy vibrates an elongated probe which transmits the acoustic energy into the fluid. The probe has a solid cleaning rod and a flared or stepped rear base. In one form, the probe is made of one piece, and in another, the rod fits into a socket in the base. This enables a rod to be made of material which is compatible with the cleaning solution, while the base may be of a different material. A heat transfer member acoustically coupled to the probe base and to a transducer conducts heat away from the transducer. A housing for the heat transfer member and the transducer supports those components and provides means for conducting coolant through the housing to control the temperature of the transducer. In another arrangement, an end of the housing is coupled between the transducer and the probe. In one arrangement, fluid is sprayed onto both sides of a wafer while a probe is positioned close to an upper side. In another arrangement, a short probe is positioned with its end face close to the surface of a wafer, and the probe is moved over the wafer as it rotates. The probe may also be positioned through a central hole in a plurality of discs to clean a group of such elements at one time.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/953,504, filed Sep. 13, 2001, now U.S. Pat. No. 6,463,938, issuedOct. 15, 2002, which is a continuation of U.S. application Ser. No.09/643,328, filed Aug. 22, 2000, now U.S. Pat. No. 6,295,999, issuedOct. 2, 2001, which is a continuation of U.S. application Ser. No.09/057,182, filed Apr. 8, 1998, now U.S. Pat. No. 6,140,744, issued Oct.31, 2000, which is a continuation-in-part of U.S. application Ser. No.08/724,518, filed Sep. 30, 1996, now U.S. Pat. No. 6,039,059, issuedMar. 21, 2000.

FIELD OF THE INVENTION

This invention relates to an apparatus and method for cleaningsemiconductor wafers or other such items requiring extremely high levelsof cleanliness.

BACKGROUND OF THE INVENTION

Semiconductor wafers are frequently cleaned in cleaning solution intowhich megasonic energy is propagated. Megasonic cleaning systems, whichoperate at a frequency over twenty times higher than ultrasonic, safelyand effectively remove particles from materials without the negativeside effects associated with ultrasonic cleaning.

Megasonic energy cleaning apparatuses typically comprise a piezoelectrictransducer coupled to a transmitter. The transducer is electricallyexcited such that it vibrates, and the transmitter transmits highfrequency energy into liquid in a processing tank. The agitation of thecleaning fluid produced by the megasonic energy loosens particles on thesemiconductor wafers. Contaminants are thus vibrated away from thesurfaces of the wafer. In one arrangement, fluid enters the wetprocessing container from the bottom of the tank and overflows thecontainer at the top. Contaminants may thus be removed from the tankthrough the overflow of the fluid and by quickly dumping the fluid.

A gas impingement and suction cleaning process for electrostatographicreproducing apparatuses which utilizes ultrasonic energy and air underpressure is disclosed in U.S. Pat. No. 4,111,546, issued to Maret.

A process for cleaning by cavitation in liquefied gas is disclosed inU.S. Pat. No. 5,316,591, issued to Chao et al. Undesired material isremoved from a substrate by introducing a liquefied gas into a cleaningchamber and exposing the liquefied gas to cavitation-producing means.The shape of the horn to provide the cavitation is not disclosed indetail and does not concentrate the sonic agitation to a particularlocation within the cleaning vessel.

In U.S. Pat. No. 4,537,511, issued to Frei, an elongated metal tube in atank of cleaning fluid is energized in the longitudinal wave mode by atransducer that extends through a wall of the tank and is attached tothe end of the tube. In order to compensate for relatively high internallosses, the radiating arrangement uses a relatively thin-walled tubularmember.

A need exists for an improved apparatus and method which can be used toclean semiconductor wafers.

SUMMARY OF THE INVENTION

The above-referenced parent patent application claims various forms ofthe invention. The present application is directed to additionalembodiments of the invention. This includes a housing having an end wallwith a vibrator or transducer, such as a piezoelectric transducercoupled to an interior surface of the end wall, while an elongated probehas an end coupled to an exterior surface of the housing end wall. Thetransducer when energized propagates megasonic energy through thehousing end wall and into the probe. The housing is preferably made ofaluminum of other material having good thermal conductivity so that heatgenerated by the transducer is dissipated through the housing.

A liquid coolant passage is formed in heat transfer relation with thehousing. Preferably, this is accomplished by positioning a heat transfermember in the housing in a manner to form the passage in combinationwith an interior wall of the housing. Coolant is then conducted throughthis passage to provide the desired cooling effect. The transducer issealed from the liquid coolant, but nitrogen or other gas may beconducted into the housing, preferably through the heat transfer member,to provide gaseous cooling for the transducer.

Preferably, the probe is coupled to the housing by positioning a layerof viscous material between the housing end wall and the probe andpressing the probe against the housing end wall. The pressing force isprovided by compressing a spring against the probe with a springretainer plate which is clamped to the housing. In addition, an O-ringsurrounds the interface between the probe and the housing end wall toconfine the viscous material and to center the probe, and is clamped inposition by a retaining ring mounted to the housing end wall.

A significant advantage of this embodiment is that the housing end wallthrough which the vibrational energy is transmitted is much thinner thanthe heat transfer member which is positioned between the probe and thetransducer in the other embodiments. This reduced mass allows increasedenergy to be transmitted to the probe with the same electrical input.The thin wall has fewer internal reflections of energy and makes tuningthe transducer easier. Nevertheless, approximately the same coolingcapacity is provided with a housing and a heat transfer member having asize comparable to that of the other embodiments.

In another embodiment, a thin wall of a heat transfer member issandwiched between the transducer and the probe. Surrounding the thinwall is an elongated annular wall of the heat transfer member, which inturn fits snugly within a surrounding cylindrical housing. A channelformed in the exterior surface of the annular wall of the heat transfermember forms a coolant passage in combination with the housing. AnO-ring surrounding the base of the probe is held in position by aretaining ring fastened to the end of the housing. Since the base orrear of the probe extends into the housing, the retainer ring includes acylindrical portion that extends into the housing to engage the O-ring.An advantage of this embodiment of the invention is that the megasonicenergy can be efficiently transmitted by the transducer through the thinwall of the heat transfer member into the probe, while at the same timeproviding excellent cooling characteristics because of a direct pathfrom the transducer through the heat transfer member to the coolingfluid passage.

Another aspect of the invention that applies to all the embodimentsdiscussed above, as well as those in the parent application, is a probemade of a base having a socket formed therein for receiving an elongatedrod portion preferably having a constant cross-section. The base and rodare coupled in a manner to efficiently transmit the megasonic energyfrom the base to the rod. An advantage of this arrangement is that asingle base can be used for rods of different materials and lengthswhich are to be contacted by a cleaning fluid. For example, a quartzbase may be used for many applications, while a rod of differentmaterial may be used with a solution containing hydrofluoric acid, whichis not compatible with quartz. Also, some materials such as vitreouscarbon can withstand most cleaning solutions but the material ispresently only readily available in constant diameter rod form.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of one embodiment of the megasonicenergy cleaning system of the present invention.

FIG. 2 is a side cross-sectional view of the system shown in FIG. 1.

FIG. 3 is an exploded perspective view of the probe assembly shown inFIG. 1.

FIG. 4 is a side view of an alternative probe in accordance with thepresent invention.

FIGS. 5a-5 c are alternative probe tips which may be used in connectionwith the present invention.

FIG. 6 is a schematic view of the probe of the present invention usedwith cleaning fluid being sprayed onto the upper surface of a wafer.

FIG. 7 is a cross-sectional view on line 7—7 of FIG. 6.

FIG. 8 is a schematic view of the probe cleaning both surfaces of awafer.

FIG. 9 is a schematic view of the probe of FIG. 1 extending throughdiscs to be cleaned.

FIG. 9a is a fragmentary, cross sectional view of a cap for a probe tip.

FIG. 9b is a fragmentary, cross sectional view of another probe tip cap.

FIG. 10 is a schematic view of a probe vertically oriented with respectto a wafer.

FIG. 11 a side elevational, partially sectionalized view of anotherembodiment of the invention having an alternate means of coupling theprobe to a support.

FIG. 12 is a side elevational, partially sectionalized view of anotherembodiment of the invention having an alternate means of mounting theprobe to the housing.

FIG. 13 is a side elevational, partially sectionalized view of anotherembodiment of the invention having an alternate arrangement for mountingthe probe and an alternate probe construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-3 illustrate a megasonic energy cleaning apparatus made inaccordance with the present invention with an elongated probe 104inserted through the wall 100 of a processing tank 101. As seen, theprobe is supported in cantilever fashion on one end exterior of thecontainer. A suitable O-ring 102, sandwiched between the probe 104 andthe tank wall, provides a proper seal for the processing tank 101. Aheat transfer member 134, contained within a housing 120, isacoustically and mechanically coupled to the probe 104. Also containedwithin the housing 120 is a piezoelectric transducer 140 acousticallycoupled to the heat transfer member 134. Electrical connectors 142, 154,and 126 are connected between the transducer 140 and a source ofacoustic energy (not shown).

The housing supports an inlet conduit 124 and an outlet conduit 122 forcoolant and has an opening 152 for electrical connectors. The housing isclosed by an annular plate 118 with an opening 132 for the probe. Theplate in turn is attached to the tank.

Within the processing tank 101, a support or susceptor 108 is positionedparallel to and in close proximity to the probe 104. The susceptor 108may take various forms, the arrangement illustrated including an outerrim 108 a supported by a plurality of spokes 108 b connected to a hub108 c supported on a shaft 110, which extends through a bottom wall ofthe processing tank 101. Outside the tank 101, the shaft 110 isconnected to a motor 112.

The elongated probe 104 is preferably made of a relatively inert,non-contaminating material, such as quartz, which efficiently transmitsacoustic energy. While utilizing a quartz probe is satisfactory for mostcleaning solutions, solutions containing hydrofluoric acid can etchquartz. Thus, a probe made of sapphire silicon carbide, boron nitride,vitreous carbon, glassy carbon coated graphite, or other suitablematerials may be employed instead of quartz. Also, quartz may be coatedby a material that can withstand HF such as silicon carbide or vitreouscarbon.

The probe 104 comprises a solid, elongated, constant cross-sectionspindle-like or rod-like cleaning portion 104 a, and a base or rearportion 104 b. The cross-section of the probe is preferably round andadvantageously, the diameter of the cleaning portion of the probe issmaller in diameter than the rear portion of the probe. In a prototypearrangement the area of the rear face of the rear portion 104 b is 25times that of the tip face of portion 104 a. Of course, cross-sectionalshapes other than circular may be employed.

A cylindrically-shaped rod portion 104 a having a small diameter isdesirable to concentrate the megasonic energy along the length of therod 104 a. The diameter of the probe, however, should be sufficient towithstand mechanical vibration produced by the megasonic energytransmitted by the probe. Preferably, the radius of the rod portion 104b should be equal to or smaller than the wavelength of the frequency ofthe energy applied to it. This structure produces a desired standingsurface wave action which directs energy radially into liquid contactingthe rod. In a prototype, the radius of the cylindrical portion of theprobe contained within the tank was approximately 0.2 of an inch andoperated at a wave length of about 0.28 of an inch. This produced 3 to 4wave lengths per inch along the rod length and has provided goodresults.

The probe cleaning portion 104 a should be long enough so that theentire surface area of the wafer is exposed to the probe during wafercleaning. In a preferred embodiment, because the wafer is rotatedbeneath the probe, the length of the cleaning portion 104 b should belong enough to reach at least the center of the wafer. Therefore, as thewafer is rotated beneath the probe, the entire surface area of the waferis close to the probe. Actually, the probe could probably functionsatisfactorily even if it does not reach the center of the wafer sincemegasonic vibration from the probe tip would provide some agitationtowards the wafer center.

The length of the probe is also determined by a predetermined number ofwavelengths usually in increments of half wavelengths of the energyapplied to the probe. In one embodiment, the length of the probecleaning portion 104 a equals nineteen wavelengths of the appliedenergy. Due to variations in transducers, it is necessary to tune thetransducer to obtain the desired wavelength, so that it works at itsmost efficient point.

The rear probe portion 104 b, which is positioned exterior the tank,flares to a diameter larger than the diameter of the cleaning portion104 a. In a first embodiment of the present invention, shown in FIGS.1-3, the diameter of the cross-section of the rear portion of the probegradually increases to a cylindrical section 104 d. The large surfacearea at the end of the rear portion 104 d is advantageous fortransmitting a large amount of megasonic energy which is thenconcentrated in the smaller diameter section 104 a.

As illustrated in FIG. 4, in an alternative embodiment of the presentinvention, the diameter of the cross-section of the rear portion of theprobe increases in stepped increments, rather than gradually. Thestepped increments occur at wavelength multiples to efficiently transmitthe megasonic energy. For example, in one embodiment, the thinnestportion 158 of the probe has a length of approximately nineteenwavelengths, the next larger diameter portion 160 is about threewavelengths in axial length and the largest diameter portion 162 isabout four wavelengths in axial length. The goal is to simulate theresults obtained with the tapered arrangement of FIG. 1.

FIGS. 5a-5 c depict further embodiments for the tip of the probe. Thedifferent probe tips may help cover a portion of the wafer surface thatotherwise would not be covered by a flat probe end 157. The probe mayhave a conical tip 164, an inverted conical tip 166, or a rounded tip168.

The probe base 104 d is acoustically coupled to a heat transfer member134 and is physically supported by that member. The probe end face ispreferably bonded or glued to the support by a suitable adhesivematerial. In addition to the bonding material, a thin metal screen 141,shown in FIG. 3, is sandwiched between the probe end and the member 134.The screen with its small holes filled with adhesive provides a morepermanent vibration connection than that obtained with the adhesive byitself. The screen utilized in a prototype arrangement was of theexpanded metal type, only about 0.002 inch thick with flattened strandsdefining pockets between strands capturing the adhesive. The adhesiveemployed was purchased from E. V. Roberts in Los Angeles and formed by aresin identified as number 5000, and a hardener identified as number 61.The screen material is sold by a U.S. company, Delkar. The probe canpossibly be clamped or otherwise coupled to the heat transfer member solong as the probe is adequately physically supported and megasonicenergy is efficiently transmitted to the probe.

As another alternative, the screen 141 may be made of a berylium copper,only about 0.001 inch thick, made by various companies using chemicalmilling-processes. One available screen holes for confining the resinthat are larger than that of the Delkar.

The heat transfer member 134 is made of aluminum, or some other goodconductor of heat and megasonic energy. In the arrangement illustrated,the heat transfer member is cylindrical and has an annular groove 136,which serves as a coolant duct large enough to provide an adequateamount of coolant to suitably cool the apparatus. Smaller annulargrooves 138, 139 on both sides of the coolant groove 136 are fitted withsuitable seals, such as O-rings 135, 137 to isolate the coolant andprevent it from interfering with the electrical connections to thetransducer 140.

The transducer 140 is bonded, glued, or otherwise acoustically coupledto the rear flat surface of the heat transfer member 134. A suitablebonding material is that identified as ECF 550, available from Ablestickof Gardena, Calif. The transducer 140 is preferably disc shaped and hasa diameter larger than the diameter of the rear end of the probe section104 d to maximize transfer of acoustic energy from the transducer to theprobe. The heat transfer member is preferably gold-plated to preventoxidizing of the aluminum and, hence, provide better bonding to thetransducer and the probe. The member 134 should have an axial thicknessthat is approximately equal to an even number of wave lengths or halfwave lengths of the energy to be applied to the probe.

The transducer 140 and the heat transfer member 134 are both containedwithin the housing 120 that is preferably cylindrical in shape. The heattransfer member is captured within an annular recess 133 in an innerwall of the housing 120.

The housing is preferably made of aluminum to facilitate heat transferto the coolant. The housing has openings 144 and 146 for the outlet 122and the inlet conduit 124 for the liquid coolant. On its closed end, thehousing 134 has an opening 152 for the electrical connections 126 and154. Openings 148, 150 allow a gaseous purge to enter and exit thehousing 120.

An open end of the housing 120 is attached to the annular plate 118having the central opening 132 through which extends the probe rearsection 104 d. The annular plate has an outer diameter extending beyondthe housing 120 and has a plurality of holes organized in two ringsthrough an inner ring of holes 131, a plurality of connectors 128, suchas screws, extend to attach the plate 118 to the housing 120. Theannular plate 118 is mounted to the tank wall 100 by a plurality ofthreaded fasteners 117 that extend through the outer ring of plate holes130 and thread into the tank wall 100. The fasteners also extend throughsleeves or spacers 116 that space the plate 118 from the tank wall. Thespacers position the transducer and flared rear portion 104 b of theprobe outside the tank so that only the cleaning portion of the probeand the probe tip extend into the tank. Also, the spacers isolate theplate 118 and the housing from the tank somewhat, so that vibration fromthe heat transfer member, the housing and the plate to the wall isminimized.

The processing tank 101 is made of material that does not contaminatethe wafer. The tank should have an inlet (not shown) for introducingfluid into the tank and an outlet (not shown) to carry away particlesremoved from the article.

As the size of semiconductor wafers increases, rather than cleaning acassette of wafers at once, it is more practical and less expensive touse a cleaning apparatus and method that cleans a single wafer at atime. Advantageously, the size of the probe of the present invention mayvary in length depending on the size of the wafer to be cleaned.

A semiconductor wafer 106 or other article to be cleaned is placed onthe support 108 within the tank 101. The wafer is positionedsufficiently close to the probe so that the agitation of the fluidbetween the probe and the wafer loosens particles on the surface of thewafer. Preferably, the distance between the probe and surface of thewafer is no greater than about 0.1 of an inch.

The motor 112 rotates the support 108 beneath the probe 104 so that theentire upper surface of the article is sufficiently close to thevibrating probe 104 to remove particles from the surface of the article.To obtain the necessary relative movement between the probe and thewafer 106, an arrangement could be provided wherein the wafer is movedtransversely beneath the probe. Also, an arrangement could be providedwherein the support 108 remains in place while a probe moves above thesurface of the wafer 106.

When the piezoelectric transducer 140 is electrically excited, itvibrates at a high frequency. Preferably the transducer is energized atmegasonic frequencies with the desired wattage consistent with the probesize length and work to be performed. The vibration is transmittedthrough the heat transfer member 134 and to the elongated probe 104. Theprobe 104 then transmits the high frequency energy into cleaning fluidbetween the probe and the wafer. One of the significant advantages ofthe arrangement is that the large rear portion of the probe canaccommodate a large transducer, and the smaller forward probe portionconcentrates the megasonic vibration into a small area so as to maximizeparticle loosening capability. Sufficient fluid substance between theprobe and the wafer will effectively transmit the energy across thesmall gap between the probe and the wafer to produce the desiredcleaning. As the surface area of the wafer 106 comes within closeproximity to the probe 104, the agitation of the fluid between the probe104 and the wafer 106 loosens particles on the semiconductor wafer 106.Contaminants are thus vibrated away from the surfaces of the wafer 106.The loosened particles may be carried away by a continued flow of fluid.

Applying significant wattage to the transducer 140 generatesconsiderable heat, which could present damage to the transducer 140.Therefore, coolant is pumped through the housing 120 to cool the member134 and, hence, the transducer.

A first coolant, preferably a liquid such as water, is introduced intoone side of the housing 120, circulates around the heat transfer member134 and exits the opposite end of the housing 120. Because the heattransfer member 134 is made of a good thermal conductor, significantquantities of heat may be easily conducted away by the liquid coolant.The rate of cooling can, of course, be readily monitored by changing theflow rate and/or temperature of the coolant.

A second, optional coolant circulates over the transducer by enteringand exiting the housing 120 through openings 148, 150 on the closed endof the housing. Due to the presence of the transducer 140 and theelectrical wiring 142, 154, an inert gas such as nitrogen is used as acoolant or as a purging gas in this portion of the housing.

An alternative arrangement for coupling the probe end 104 b to themember 134 is illustrated in FIG. 11. Instead of having the probe bondedto the member 134, a so-called vacuum grease is applied to the screen141, and the probe is pressed against the member 134 by a coil spring143. Vacuum grease is a viscous grease which can withstand pressures onopposite sides of a joint without leaking or being readily displaced. Ina prototype arrangement, the combination of the grease and the metalspring provided a reliable acoustic coupling. As may be seen in FIG. 11,the housing 120 instead of being mounted directly to the plate 118, ismounted by standoffs 16 to the plate 118. The sleeves 116 and thefasteners 117 are shorter than that shown in FIG. 2, such that the plate118 surrounds the tapered portion of the probe. This leaves a gapbetween the housing 120 and the plate 118. The coil spring 143 ispositioned in this gap and compressed between the plate 118 and thetapered portion of the probe. Thus, the spring presses the probe towardthe member 134. This arrangement acoustically couples the probe to theheat transfer member 134. A Teflon sleeve 149 is preferably positionedover the first coil of the spring 143 adjacent the probe so that themetal spring does not damage the quartz probe.

An arrangement is illustrated in FIG. 6, wherein the probe assembly ofFIG. 1 is shown in conjunction with a tank 200 which is open on itsupper end and has a drain line 202 in its lower end. The probe 104 isshown extending through a slot 203 into the tank above a wafer 106mounted on a suitable support 208 including an annular rim 208 a, aplurality of spokes 208 b, joined to a hub 208 c positioned on the upperend of a shaft 210 rotated by a motor 212.

In use, deionized water or other cleaning solution is sprayed onto theupper surface of the wafer from a nozzle 214 while the probe 104 isbeing acoustically energized. The liquid creates a meniscus 115 betweenthe lower portion of the probe and the adjacent upper surface of therotating wafer. This is schematically illustrated in FIG. 7. The liquidprovides a medium through which the megasonic energy is transmitted tothe surface of the wafer to loosen particles. These loosened particlesare flushed away by the continuously flowing spray and the rotatingwafer. When the liquid flow is interrupted, a certain amount of dryingaction is obtained through centrifical force of the liquid off of thewater.

The probe assembly may be conveniently mounted on a suitable support,schematically illustrated at 216. The support is capable of pivoting theassembly upwardly, as indicated by the arrow in FIG. 6, to facilitatethe installation and removal of wafers. Alternatively, the slot 203 mayinstead be formed as a hole, closed at the top, and the probe may bemoved radially in and out.

FIG. 8 illustrates an alternative or addition to the arrangement of FIG.7 wherein both the lower and upper sides of a wafer are cleaned. A spraynozzle 254 extends through a side wall of a tank 200 and is angledupwardly slightly so that cleaning fluid may be sprayed between thespokes 208 b and onto the lower surface of a wafer 106 and is directedradially inwardly so that as the wafer rotates, the entire lower surfaceis sprayed with the fluid. The wafer is subjected to megasonic energy bythe probe 104 in the same manner as described above in connection withFIG. 6. This agitation vibrates the wafer as well as the fluid on thelower surface of the wafer which is radially aligned with the probe asthe wafer rotates. This agitation loosens particles on the lower surfaceof the wafer, and the particles are flushed away with the fluid whichfalls or drips from the lower surface of the wafer.

Various fluids may be employed as the spray applied to the wafer inFIGS. 6 and 8. In addition to liquid or high pressure gas, so-called dryice snow may be applied. Va-Tran Systems, Inc. of Chula Vista, Calif.markets a product under the trademark SNO GUN for producing and applyingsuch material. A major advantage of that approach is that there is nodisposal problem after cleaning. Contamination is carried away from theclean surface in a stream of inert, harmless vapor. Disposal costs ofcleaning media are eliminated. Advertising literature regarding the SNOGUN product states that cleaning with dry ice snow removes particlesmore thoroughly than blowing with dry nitrogen. It is said that thedevice removes even sub-micron particles as tiny as 0.2 microns, whichare difficult or impossible to remove with a nitrogen jet. Suchtechnology is further described in U.S. Pat. No. 5,364,474, which isincorporated herein by reference.

Referring to FIG. 9, the probe assembly of FIG. 1 is shown mounted to awall of a tank 300. The probe 104 extends generally horizontally throughcentral openings in a plurality of vertically orientated substrates suchas “compact discs” 302. The discs may be mounted in a cassette immersedin the tank with the holes in the discs aligned with the probe. Thecassette carrying the discs can then be moved laterally so that theprobe extends through the holes in the discs, without actuallycontacting the discs. The tank is filled with liquid, such as deionizedwater to completely cover the discs. The probe is then vibrated bymegasonic energy in the manner described above in connection with FIG.1. The agitation produced by the probe is transmitted into the cleaningliquid between the discs to loosen particles on the surfaces of thediscs. The energy propagates radially outward from the probe such thatboth sides of each disc are exposed to such energy. Cleaning liquid maybe introduced into the container in continuous flow and allowed tooverflow the upper end of the container to carry away loosenedparticles.

Because some megasonic energy will be transmitted through the end of theprobe with the probe tip immersed in the liquid, a small cap 306 ispositioned on the tip of the probe with the cap containing an air space308 between two glass walls 306 a and 306 b, as shown in FIG. 9a. Sincemegasonic energy does not travel through ambient air to any significantdegree, the cap prevents the loss of energy through the end of theprobe. An alternative cap 310 shown in FIG. 9b employs a short sectionof glass tubing 212 attached to the end of the probe. As seen, the outerdiameter of the tube is equal to the outer diameter of the probe, andthe outer end of the tube spaced from the probe is closed by a disc 314.

FIG. 10 illustrates another embodiment of the probe of the invention. Aprobe assembly 400 is shown which is similar to the assembly of FIG. 1except that the probe 404 is much shorter than the probe 104 in FIG. 1.In addition, the assembly 400 is oriented with the probe extendinggenerally vertically, generally perpendicular to the surface of thehorizontal wafer 106. Cleaning fluid is applied to the upper surface ofthe wafer, and the lower tip of the probe is in contact with this fluid.Consequently, megasonic energy is transmitted through this medium ontothe surface of the wafer causing loosening of particles. Since the sidesof the probe are not exposed to this medium, there is no appreciablemegasonic energy transmitted from the vertical sides of the probe.Instead, such megasonic energy is concentrated into the tip. The tip canbe moved radially with respect to the wafer as the wafer rotates so asto apply megasonic energy to the entire surface of the wafer.Alternatively, the probe may traverse the entire upper surface. Anysuitable support 410 containing a mechanism to provide the desiredmovement may be employed.

As mentioned above, the preferred form of the probe assembly includes aprobe made of inert material such as quartz and a heat transfer membercoupled to the rear of the probe made of a good heat conducting materialsuch as aluminum. Since it is the cylindrical portion of the probe whichis in contact with the cleaning fluid and is positioned adjacent thewafer, an alternative arrangement could be devised wherein a forwardportion, such as section 104 a in FIG. 1 could be made of the inertmaterial and the rear portion 104 b could be made of aluminum and hencecould be made as one piece with the heat transfer member 134. This ofcourse means that the joint between the two components would be at therear of the cylindrical portion 104 a. While such a bonding area wouldnot be as strong as the arrangement illustrated in FIG. 1, it may beuseful in certain situations.

In the other direction, there may be some applications in which it isnot necessary to employ quartz or other such inert material for theprobe. Instead, the entire probe could be made of aluminum or other suchmaterial. In that situation, the heat transfer member could then be madeas a one-piece unit with the probe. Also, with a metal probe it may bepractical to spray the cleaning fluid through the probe itself. Forexample in the arrangement of FIG. 10, fluid inlet could be located inthe side of the large diameter end of the probe and an outlet can belocated in the end face of the small diameter probe end. The fluid wouldalso serve as a coolant to cool the transducer, particularly if dry icesnow were employed.

The embodiment of FIG. 12 has a number of similarities to the otherembodiments, but has some important distinctions. That arrangementincludes a cup-shaped housing 520 similar to the housing 120 in FIG. 2,but inverted with respect to the housing 120. The housing 520 includes aclosed end wall 520 a having a surface 520 b facing the interior of thehousing 520 and having an exterior surface 520 c facing away from thehousing. Coupled to the interior end wall surface 520 b is a disc-shapedtransducer 540 analogous to the transducer 140 referred to above inconnection with FIGS. 2 and 3. The transducer 540 is preferably bondedto the wall surface 520 b in the same manner mentioned above inconnection with FIGS. 2 and 3.

The large end 504 b of a probe 504 is acoustically coupled to thehousing end wall exterior surface 520 c. The acoustic coupling isaccomplished by the use of a coil spring 543 surrounding the probe 504and reacting against the spring retainer plate 518 to press the largeend 504 b of the probe towards the housing end wall 520 a. As discussedin connection with FIG. 3, a screen 141, together with an appropriateviscous material, is sandwiched between the large end of the probe andthe end wall 520 a. The coil spring adjacent the large end of the probehas a sleeve or sleeve portions 544 made of a material which will notdamage the probe. The O-ring is held in place and compressed against theend wall 520 a and the probe by a retainer ring 519 having a surface 519a which presses against the O-ring. The O-ring thus prevents the escapeof the viscous material from between the probe and the housing end wall,and centers the probe. The retainer ring is attached to the housing by aplurality of bolts 525 which extend through the retainer ring and threadinto the housing. The spring 543 is captured and compressed by areaction plate 518 which surrounds the probe and is attached to thehousing by a plurality of fasteners 528 which thread into the retainerring 519 and are spaced from it by sleeves 516 surrounding the fasteners528. For convenience of illustration, the fasteners 525 and 528 are allshown in the same plane in FIG. 12. In actual practice, the fasteners528 would preferably be on the same bolt hole diameter as the fasteners525, and they of course would be spaced with respect to the fasteners525. Also, the fasteners would not necessarily be spaced 180E apart asillustrated, but would be spaced in whatever manner is practical.

Positioned within the cup-shaped housing 520 is an annular heat transfermember 534 which has an external diameter sized to fit snugly within thehousing 520. An annular groove 536 in the exterior of the heat transfermember 534, creates a liquid cooling channel in combination with theinner surface of the housing 520. A pair of O-rings 537 that fit withinannular grooves in the heat transfer member seal the coolant channel 536so that the remainder of the interior of the housing is sealed from theliquid. This prevents interference with the electrical energy beingsupplied to the transducer. Further, transducer vibration energy is notdissipated into the interior of the housing, but instead is transmittedinto the housing end wall 520 a and into the probe 504. The heattransfer member 534 is axially captured within the housing by means ofan annular shoulder 520 d and by a housing end plate 560. A plurality offasteners 528 connect the plate 560 to the housing. A liquid coolantinlet 562 a is mounted in an opening in the end plate 560 and threadsinto a passage 519 in the heat transfer member that extends axially andthen radially into the annular channel 536. A similar outlet fitting 562b mounts in the end plate 560 diametrically opposed from the 562 afitting, and threads into another passage 519 that extends axially andradially into the channel 536.

A plurality of axially extending bores 563 are also formed in the heattransfer member 534, aligned with gas inlets 561 formed in the plate560. The inlets 561 and bores 563 are shown in the same plane with thepassages 519 for convenience. In actual practice, the bores 563 wouldpreferably not be in the same plane as the passages 519, and insteadwould be circumferentially offset, and could also be formed in the samecircle around the center of the heat transfer member 534. The inlets 561through the end plate 560 for the fittings 562 a and 562 b wouldlikewise be moved to be aligned with the passages 563.

The electrical connection for the transducer 540 is illustrated by thewire 554, although the more complete connection would be as shown inFIG. 3. That wire extends through a fitting 528 which in turn isconnected to an electrical cord 526.

In operation, there are a number of advantages to the embodimentillustrated in FIG. 12. By coupling the transducer and the probe to thehousing end wall, more energy may be transmitted to the probe than withthe corresponding amount of power applied to the transducer in thearrangement of FIG. 2, inasmuch as the housing end wall has less massthan the mass of the heat transfer member 140 shown in FIG. 3. Whilesome energy is lost into the other portions of the housing, there is anet increase in efficiency. The relatively thin end wall has fewerinternal energy reflections than a thicker wall simply because of thereduced mass. However, in addition the housing end wall does not havethe discontinuities caused by the grooves in the heat transfer member ofFIG. 2, or by the O-ring in the grooves.

By making the housing 520 of aluminum or other material which is arelatively good thermal energy conductor, the heat generated by thetransducer can be readily dissipated with the arrangement of FIG. 12.The heat transfer member 534 can be made of the desired axial lengthwithout concern for its mass because it is not to be vibrated as in thearrangement of FIG. 2. The cooling liquid enters through the fitting 562a, flows axially and then radially into the channel 536, where it splitsinto two branch flows in opposite directions, that meet on the otherside of the heat transfer member and flow out the fitting 562 b.

Similarly, cooling gas such as nitrogen can be connected to one or moreof the bores 563 in the heat transfer member and into the central areaof the housing. The gas is exhausted through one of the bores 563leading to a second outlet 561 b. Two passages 563 are illustrated inFIG. 12. Three are preferable, but more or less may be utilized ifdesired. To perform an additional function, bolts may be threaded intothe bores 563 to assist in withdrawing the heat transfer member from thehousing.

The assembly illustrated in FIG. 12 may be used in connection with awall mounted arrangement such as that shown in FIG. 1, or may be usedwith a system such as that as illustrated in FIG. 8, wherein the probeassembly is moved into or out of position with respect to a wafer tofacilitate insertion and removal of wafers. As mentioned above, such aprobe may be moved out of the way by mounting it on a bracket that willpivot it in the direction of the arrow 218 shown in FIG. 8, or it may beon a track arrangement (not shown) which will move it radially inwardlyand outwardly with respect to the wafer and its supporting member. Theassembly of FIG. 12 may be mounted to these other structures in anysuitable fashion, such as by making connections to the end plate 560.

The arrangement of FIG. 13 includes a generally tubular or cylindricalhousing 620. Positioned within the housing is a heat transfer member 634having an outer annular wall 634 a which fits snugly within asurrounding annular wall of the housing 620. The heat transfer member634 has an annular channel 636 formed in its outer surface that facesthe surrounding housing wall to form a coolant passage. A coolant inlet644 in the housing wall leads into the passage and an outlet 646 on theopposite side of the housing leads out of the passage.

As seen in FIG. 13, the heat transfer member 634 has somewhat of anH-shaped cross section created by a central disc-shaped wall 634 bintegrally formed with the surrounding annular wall 634 a. As seen, thecentral wall 634 b is relatively thin and it is radially aligned withthe surrounding coolant passage 636. The heat transfer member is axiallycaptured within the housing by an internal shoulder on one end of thehousing and by an end plate 660 on the other end.

A piezoelectric transducer 640 is acoustically coupled to one side ofthe central wall 634 b, such as in the same manner discussed above inconnection with the other embodiments. A probe 604 is acousticallycoupled to the other side of the central wall 634 b. Again, this may bedone in various ways, such as the screen and grease technique discussedabove. An O-ring 621 surrounds the base of the probe and is compressedagainst the probe and the central wall 634 b by a cylindrical portion ofan end member 619 having a flange attached to the end of the housing620. The O-ring confines the coupling grease and helps center the probe604. The probe is pressed against the central wall 634 b by a spring 643compressed between an annular spring retainer plate 18 and the probe604.

The housing and heat transfer member illustrated in FIG. 13 may be usedwith the probes illustrated in the above-mentioned embodiments, but itis illustrated in FIG. 13 with an alternate probe construction. Insteadof having the probe made of one piece, it is formed in separate portionsincluding a base 605 adjacent the central wall 634 b of the heattransfer member, and an elongated cleaning rod 606. The base 605 has acylindrical exterior with a reduced diameter portion 605 a on the endspaced from the central wall 634 b. One end of the spring 643 surroundsthe base portion 605 a and engages the shoulder on the base 605 adjacentthe portion 605 a. The rod 606 of the probe fits within a central socketformed in the base 605. It is bonded to the base by a suitable adhesivewhich will not interfere with the transmission of the megasonic energyprovided by the transducer 640 and propagated through the central wall634 b and the base 605 of the probe.

The base 605 can have a frusto-conical configuration just as the rearportion of the probe in FIG. 12, and the spring 643 could then engagethe sloping side wall of such shape rather than having the stepconfiguration shown in FIG. 13. Also, in theory, the rod 606 could havea tapered end and the spring could engage it as suggested by FIG. 12.

A primary purpose of having a probe made of two different portions isthat one portion can be made of a different material from the other. Forexample, the base 605 can be utilized in any cleaning operation since itdoes not contact the cleaning solution; however, the rod 606 must becompatible with the cleaning solution. Thus, if the cleaning solution iscompatible with quartz, a one-piece arrangement such as that illustratedin FIG. 1 or FIG. 12 could be conveniently utilized. If, however, thecleaning solution is not compatible with quartz, such as a solutioncontaining hydrofluoric acid, a material for the rod is needed that iscompatible, such as vitreous carbon, while the base can be quartz. It iscurrently difficult to obtain vitreous carbon in a shape such as thatillustrated in FIG. 12. However, a straight cylindrical rod is morereadily available. Hence, it is practical to utilize it in thearrangement illustrated in FIG. 13. Of course any other desirablecombination of suitable materials for the rod and the base may beemployed.

As mentioned above, the arrangement of FIG. 13 is particularly desirablefrom the standpoint that the transmission of megasonic energy isefficient through the thin wall portion of the heat exchange member, butyet the heat exchange process is very efficient. This is because thetransducer, which is the heat generator, is in direct contact with theheat transfer member, which is in direct contact with the coolantpassage 636. It should be recognized that other heat transferarrangements may be employed. For example, if the heat transfer memberhas sufficient surface area, it might be possible to have it air-cooledrather than liquid-cooled. It should also be recognized that variousother modifications of that type may be made to the embodimentsillustrated without departing from the scope of the invention, and allsuch changes are intended to fall within the scope of the invention, asdefined by the appended claims.

What is claimed is:
 1. An apparatus for processing a thin, flatsubstrate, comprising: a support for engaging the periphery of a thin,planar substrate for supporting the substrate in a substantiallyhorizontal orientation; a first source for applying only-a thin film ofliquid to one side of the substrate while on said support in saidorientation; a second source for applying a thin film of liquid to anopposite side of the substrate in said orientation; and a transmitter tobe positioned close to the substrate in contact with one of said filmsto apply sonic energy to the substrate through said one film and throughsaid substrate to the other film to loosen particles on both sides ofthe substrate simultaneously, while maintaining said orientation.
 2. Theapparatus of claim 1, wherein said first source is a conduit.
 3. Theapparatus of claim 2, wherein said second source is a conduit.
 4. Theapparatus of claim 1, wherein said first source is a sprayer.
 5. Anapparatus for cleaning a semiconductor wafer, comprising: a supportsupporting the wafer in a horizontal orientation; means for applying athin film of liquid to top and bottom sides of the wafer; and atransmitter positioned close to the wafer to apply megasonic energy tothe wafer through the film on one of said sides and through said waferto the other film to loosen particles on both sides of the wafersimultaneously while maintaining said orientation.
 6. Apparatus forcleaning a thin article having two substantially planar opposite sides,comprising: a support for supporting the article in a orientation aconduit for applying only-a thin film of fluid to one of said sides; anda transmitter configured to apply vibration to the other one of saidsides with sufficient power to produce vibration in said article and insaid fluid film to loosen particles on said one side, while maintainingsaid orientation.
 7. The apparatus of claim 6, including a conduit forapplying the film of fluid to said other side adjacent to and in contactwith said transmitter to couple the vibration of the transmitter throughthe fluid applied to said other side so as to loosen particles on bothsides of the article.
 8. The apparatus of claim 6, including atransducer for vibrating the transmitter and wherein said transmitter isformed of quartz, sapphire, silicon carbide, silicon nitride, quartzcoated with silicon carbide or quartz coated with vitreous carbon. 9.The apparatus of claim 6, wherein said support is configured to supportthe article in a substantially horizontal position and so that the lowerside of the article positioned on the support is accessible so thatfluid can be applied to the lower side.
 10. Apparatus for cleaning athin article having two substantially planar opposite sides, comprising:a support for the article; a conduit for applying fluid to one of saidsides; a transmitter configured to apply vibration to the other one ofsaid sides with sufficient power to produce vibration in said articleand in said fluid to loosen particles on said one side; a transducer forvibrating the transmitter; and a wall with an opening therein throughwhich gas is introduced to flow in contact with said transducer. 11.Apparatus for cleaning a thin article having two substantially planaropposite sides, comprising: a support for the article; a conduit forapplying fluid to one of said sides; a transmitter configured to applyvibration to the other one of said sides with sufficient power toproduce vibration in said article and in said fluid to loosen particleson said one side; a transducer for vibrating the transmitter; and apassage for inert gas to flow in contact with said transducer to purgean area adjacent to said transducer or to cool said transducer. 12.Apparatus for cleaning a thin article having two substantially planaropposite sides, comprising: a support for the article; a conduit forapplying fluid to one of said sides; a transmitter configured to applyvibration to the other one of said sides with sufficient power toproduce vibration in said article and in said fluid to loosen particleson said one side; a transducer for vibrating the transmitter; and anenclosure creating a space in contact with said transducer, with anopening in said enclosure for introducing gas into said space.